The use of endovascular techniques for the implantation of medical devices and the occlusion of body cavities such as arteries, veins, fallopian tubes or vascular deformities is known in the art. For example, occlusion of vascular aneurysms can be performed using an implantable device, such as an occlusion spiral, that is introduced with the aid of an endovascular guide wire through a catheter. Once moved to the treatment site, the occlusion spiral can be moved into the aneurysm cavity to occlude the aneurysm.
The severance of the occluding spiral from the endovascular guide wire can be particular technically problematic. On the one hand, the device must be as small as possible to be guided through the fine bore of the catheter to its destination, while on the other hand it must bring about a reliable severance of the occluding spiral. Absent a reliable severance of the occluding spiral, withdrawal of the guide wire and catheter may cause unintended removal of the occluding spiral from the cavity to be occluded and thus injure and/or rupture of the wall of the cavity or vessel.
Mechanical methods for the severance of occluding spirals from the insertion means do not take much time to perform. However, the necessary rigidity of the technical features of the connection between the occluding spiral and the introduction means impede the introduction of the implant. Furthermore, the low load carrying capacity of the connection due to its rigidity entails a not inappreciable risk of premature detachment of the insertion means from the occluding implant. Moreover, in the case of mechanical separation of the inserting wire and the occluding spiral, energy must be transmitted (as a rule by rotation of the inserting wire), and this may mean that the implant is dislodged out of the correct position.
Electrolytic severance of the occluding spiral involves using an electrolytically corrodible design on the end of the guide wire at the connection between the guide wire and the occluding spiral. Such a device can elegantly makes use of the voltage applied to the occluding spiral serving as an anode for electro-thrombization. However, for the simultaneous severance of the wire end and the occluding spiral thereon, such a device suffers, just like the above-mentioned mechanical severance method, from the disadvantage that only implants of predetermined length can be detached or severed. It has therefore been considered generally necessary that the doctor determine the length or longitudinal extent of the occluding spiral directly prior to the insertion of the implant, on the basis of the size of the cavity to be occluded. Since the irregular form of body cavities to be occluded makes it difficult to correctly assess the length of the occluding spiral necessary for filling, there is the likelihood of excessively long or excessively short occluding spirals being introduced into the cavity to be occluded, something which may involve on the one hand an incomplete occlusion or on the other hand injury to or rupture of the wall of the cavity (or of contiguous vessels) to be occluded.
A further disadvantage of the electrolytic severance of the end of the guide wire is that for production of the guide wire, the only materials that can be utilized are those which have a sufficiently high degree of strength to enable reliable guidance of the occluding wire through the guide wire. The selection of materials for forming the point of eventual electrolytic severance is consequently extremely limited.
In the case of prior art devices for the electrolytic severance of occluding spirals, the occluding spiral and the guide wire are not produced integrally, but instead are produced mechanically connected with each other. This design has the inherent disadvantage that the guide wire must be tapered toward its end in an involved grinding operation in order to ensure sufficient strength in the proximal zone of the guide wire and to facilitate electrolytic, corrosive severance of the wire end in the distal part of the guide wire. In order to ensure sufficient strength of the connection point, the corrodible zone of the end of the guide wire must not have a diameter below a certain minimum value since it is subjected to a high flexural load. The corrodible wire end representing the connection point between the occluding spiral and the guide wire can be consequently extremely rigid and require a relatively long time for electrolytic corrosive severance.